Increasingly rapid consumption of natural resources and the production of wastes and their impacts on ecosystems have become unsustainable practices due to the increase in population, technological development and economic growth. The role of environmental education (EE) has been highlighted for promoting more sustainable ways of living by improving knowledge, behaviour and action to address environmental challenges and help society to shift toward sustainability. Environmental education is positioned in New Zealand education as an interdisciplinary teaching and learning approach. The non-mandatory status of EE emphasises an holistic approach to meeting the aims of EE. However, teachers face some challenges integrating the complex and evolving content of EE into school curricula due to lack of support and professional learning opportunities. Collaboration for teachers could help them to share their experiences with challenges regarding teaching and learning in EE. Building connections between teachers could help them to increase their knowledge and enhance their teaching practice, which in turn could affect students’ learning. Social media is used for collaborative learning in diverse disciplines for various purposes. It has the potential to be used for teacher professional learning (TPL) as communication and resources can be combined to create collaborative learning opportunities. However, there is little evidence to date of its use in TPL in EE. Considering the advantages and the possibility of social media for use in TPL in EE, the purpose of this study was to explore teachers’ perceptions of professional learning through social media in EE in New Zealand. A mixed method study was designed and conducted in three phases using a phenomenographic approach. Findings from questionnaires and interviews in the first and second phases suggested that teachers see TPL through social media as potentially collaborative, convenient, and ubiquitous. They also believed building connections through social media can help EE teachers interact with peers and experts, as well as access support and resources to enhance their teaching practice. Despite these benefits, some teachers perceived this kind of TPL to be challenging. Time for engagement, the accuracy of shared information, privacy of participation, unfocused information and the conflict between online learning and EE as a practical subject were mentioned as the barriers of learning through social media. Specifically, the lack of educational support and lack of TPL were identified as challenges for secondary teachers who engaged with Achievement Standards related to education for sustainability (EfS). These findings were used to design and establish a learning community for secondary school teachers through Google+ in the third phase. The Google+ Community facilitated synchronous and asynchronous interactions between teachers and EE experts in different locations. Teachers, however, were not fully engaged in community activities. Findings from interviews and document analysis in the third phase suggested that some limitations associated with the community coupled with teachers’ priorities shaped participants’ involvement in the community. Participants claimed that they needed motivation and time to become actively engaged in the community. This research contributes to an understanding of teachers’ perceptions and experiences of professional learning through social media in EE. Insights gained from this study relate to both possibilities and challenges of learning through social media. It also highlights the vital role EE stakeholders play in TPL in EE and their influence on teachers’ motivation. A number of strategies that are suggested at the end of this thesis can be of use in designing TPL in general, TPL in EE, and TPL through social media in particular.